Optical imaging system

ABSTRACT

An optical imaging system includes a first lens, a second lens, a third lens, a fourth lens, a fifth lens, a sixth lens, and a seventh lens sequentially disposed in ascending numerical order along an optical axis from an object side of the optical imaging system toward an imaging plane of the optical imaging system. Four or more lenses among the first to seventh lenses have a refractive index greater than 1.6.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of application Ser. No. 17/070,203 filed on Oct. 14, 2020, which is a continuation of application Ser. No. 16/278,913 filed on Feb. 19, 2019, now U.S. Pat. No. 10,838,176 issued on Nov. 17, 2020, which is a continuation of application Ser. No. 15/586,351 filed on May 4, 2017, now U.S. Pat. No. 10,247,916 issued on Apr. 2, 2019, and claims the benefit under 35 USC 119(a) of Korean Patent Application No. 10-2016-0179151 filed on Dec. 26, 2016, in the Korean Intellectual Property Office, the entire disclosures of which are incorporated herein by reference for all purposes.

BACKGROUND 1. Field

The following description relates to a telescopic optical imaging system including seven lenses.

2. Description of Related Art

In small cameras, the size of a pixel in an image sensor is reduced when the camera's resolution is improved. In detail, image sensors of cameras implementing a high resolution, of 12 megapixels or greater, may include pixels smaller than that of image sensors of cameras implementing a resolution of 8 megapixels. Because such pixels lead to a reduced amount of light incident on each pixel in the image sensors, the implementation of clear and bright images is difficult. Thus, optical imaging systems capable of improving the resolution and brightness of small cameras are being developed.

SUMMARY

This Summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This Summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter.

In one general aspect, an optical imaging system includes a first lens having a positive refractive power, a second lens a refractive index of 1.65 or greater, a third lens having a positive refractive power and a refractive index of 1.65 or greater, a fourth lens having a positive refractive power, a fifth lens having a refractive index of 1.65 or greater, a sixth lens having a refractive index of 1.65 or greater, and a seventh lens having a positive refractive power. The first to seventh lenses are sequentially disposed from an object side to an imaging plane.

The first to seventh lenses of the optical imaging system may be formed using a plastic material. The first lens of the optical imaging system may have a convex object-side surface and a concave image-side surface along an optical axis. The second lens of the optical imaging system can have a convex object-side surface and a concave image-side surface along an optical axis. The third lens of the optical imaging system may have a convex object-side surface and a concave image-side surface along an optical axis.

The fourth lens of the optical imaging system can have opposing convex surfaces along an optical axis. The fifth lens of the optical imaging system may have a convex object-side surface and a concave image-side surface along an optical axis. The sixth lens of the optical imaging system can have a convex object-side surface and a concave image-side surface along an optical axis. The seventh lens of the optical imaging system may have a convex object-side surface and a concave image-side surface along an optical axis.

The optical imaging system may satisfy the expression V2+V3<V1, where V1 represents an Abbe number of the first lens, V2 represents an Abbe number of the second lens, and V3 represents an Abbe number of the third lens. The optical imaging system can satisfy the expression V5+V6<V4, where V4 represents an Abbe number of the fourth lens, V5 represents an Abbe number of the fifth lens, and V6 represents an Abbe number of the sixth lens. The optical imaging system may satisfy the expression CT2<0.2 mm, where CT2 represents a thickness of the second lens. The optical imaging system can have an F number that is less than or equal to 2.09.

In another general aspect, an optical imaging system includes a first lens having a positive refractive power, a second lens having a refractive index greater than or equal to 1.65, a third lens having a positive refractive power and a refractive index greater than or equal to 1.65, a fourth lens having a positive refractive power, a fifth lens having a refractive index greater than or equal to 1.65, a sixth lens having a refractive index greater than or equal to 1.65, and a seventh lens having a positive refractive power. The first to seventh lenses are sequentially disposed from an object side to an imaging plane.

The sixth lens of the optical imaging system may include an inflection point formed on one or both of an object-side surface or an image-side surface. The seventh lens of the optical imaging system can include an inflection point formed on one or both of an object-side surface or an image-side surface.

In another general aspect, an optical imaging system includes a first lens having a positive refractive power, a second lens having a negative refractive power, a third lens having a positive refractive power, a fourth lens having a positive refractive power, a fifth lens having a positive refractive power, a sixth lens having a negative refractive power, and a seventh lens having a positive refractive power. The first to seventh lenses are sequentially disposed from an object side to an imaging plane. The second lens, the third lens, the fifth lens, and the sixth lens each have a refractive index greater than or equal to 1.65. An F number of the optical imaging system is less than or equal to 2.09.

The first lens, the second lens, the fourth lens, and the seventh lens of the optical imaging system may each include a convex object-side surface along an optical axis. The optical imaging system can satisfy the expression 1.0<TTL/f, where TTL represents a distance from an object-side surface of the first lens to an imaging plane and f represents a focal length of the optical imaging system.

Other features and aspects will be apparent from the following detailed description, the drawings, and the claims.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram of an optical imaging system according to a first example.

FIG. 2 is a set of graphs illustrating aberration curves of the optical imaging system illustrated in FIG. 1 .

FIG. 3 is a table listing aspherical characteristics of the optical imaging system illustrated in FIG. 1 .

FIG. 4 is a diagram of an optical imaging system according to a second example.

FIG. 5 is a set of graphs illustrating aberration curves of the optical imaging system illustrated in FIG. 4 .

FIG. 6 is a table listing aspherical characteristics of the optical imaging system illustrated in FIG. 4 .

FIG. 7 is a diagram of an optical imaging system according to a third example.

FIG. 8 is a set of graphs illustrating aberration curves of the optical imaging system illustrated in FIG. 7 .

FIG. 9 is a table listing aspherical characteristics of the optical imaging system illustrated in FIG. 7 .

Throughout the drawings and the detailed description, the same reference numerals refer to the same elements, where applicable. The drawings may not be to scale, and the relative size, proportions, and depiction of elements in the drawings may be exaggerated for clarity, illustration, or convenience.

DETAILED DESCRIPTION

Hereinafter, examples will be described with reference to the attached drawings. Examples provide a high-resolution, bright optical imaging system capable of being mounted in a small terminal. The disclosure may, however, be exemplified in many different forms and should not be construed as being limited to the specific embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure after an understanding of the application.

Throughout the specification, it will be understood that when an element, such as a layer, region or wafer (substrate), is referred to as being “on,” “connected to,” or “coupled to” another element, it can be directly “on,” “connected to,” or “coupled to” the other element, or other elements intervening therebetween may be present. In contrast, when an element is referred to as being “directly on,” “directly connected to,” or “directly coupled to” another element, there may be no elements or layers intervening therebetween. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items.

Although terms such as “first,” “second,” and “third” may be used herein to describe various components, regions, or sections, these components, regions, or sections are not to be limited by these terms. Rather, these terms are only used to distinguish one component, region, or section from another component, region, or section. Thus, a first component, region, or section referred to in examples described herein may also be referred to as a second component, region, or section without departing from the teachings of the examples.

The articles “a,” “an,” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. The terms “comprises,” “includes,” and “has” specify the presence of stated features, numbers, operations, members, elements, and/or combinations thereof, but do not preclude the presence or addition of one or more other features, numbers, operations, members, elements, and/or combinations thereof.

Due to manufacturing techniques and/or tolerances, variations of the shapes shown in the drawings may occur. Thus, the examples described herein are not limited to the specific shapes shown in the drawings, but include changes in shape that occur during manufacturing.

The features of the examples described herein may be combined in various ways as will be apparent after an understanding of the disclosure of this application. Further, although the examples described herein have a variety of configurations, other configurations are possible as will be apparent after an understanding of the disclosure of this application.

In the present specification, a first lens refers to a lens closest to an object or a subject of which an image is captured. A seventh lens refers to a lens closest to an imaging plane or an image sensor. In the present specification, an entirety of a radius of curvature, a thickness, a distance from an object-side surface of a first lens to an imaging plane (TTL), a half diagonal length of the imaging plane (IMG HT), and a focal length of a lens is indicated in millimeters (mm). A person skilled in the relevant art will appreciate that other units of measurement may be used. Further, in embodiments, all radii of curvature, thicknesses, OALs (optical axis distances from the first surface of the first lens to the image sensor), a distance on the optical axis between the stop and the image sensor (SLs), image heights (IMGHs) (image heights), and back focus lengths (BFLs) of the lenses, an overall focal length of an optical system, and a focal length of each lens are indicated in millimeters (mm). Likewise, thicknesses of lenses, gaps between the lenses, OALs, TLs, SLs are distances measured based on an optical axis of the lenses.

In a description of a form of a lens, a surface of a lens being convex means that an optical axis portion of a corresponding surface is convex, while a surface of a lens being concave means that an optical axis portion of a corresponding surface is concave. Therefore, in a configuration in which a surface of a lens is described as being convex, an edge portion of the lens may be concave. In a manner the same as the case described above, even in a configuration in which a surface of a lens is described as being concave, an edge portion of the lens may be convex. In other words, a paraxial region of a lens may be convex, while the remaining portion of the lens outside the paraxial region is either convex, concave, or flat. Further, a paraxial region of a lens may be concave, while the remaining portion of the lens outside the paraxial region is either convex, concave, or flat. In addition, in an embodiment, thicknesses and radii of curvatures of lenses are measured in relation to optical axes of the corresponding lenses.

In accordance with illustrative examples, the embodiments described of the optical system include seven lenses with a refractive power. However, the number of lenses in the optical system may vary in some embodiments, for example, between two to seven lenses, while achieving one or more results and benefits described below. Also, although each lens is described with a particular refractive power, a different refractive power for at least one of the lenses may be used to achieve the intended result.

An optical imaging system includes seven lenses. For example, the optical imaging system may include the first lens, a second lens, a third lens, a fourth lens, a fifth lens, a sixth lens, and the seventh lens, sequentially disposed from an object side to an imaging plane.

The first lens has a refractive power. For example, the first lens has a positive refractive power. The first lens has a convex surface. In an embodiment, the first lens has a convex object-side surface.

The first lens has an aspherical surface. For example, both surfaces of the first lens are aspherical. The first lens may be formed using a material having a relatively high degree of light transmittance and excellent workability. In an example, the first lens is formed using a plastic material. The first lens has a relatively low refractive index. In an embodiment, a refractive index of the first lens is less than 1.6.

The second lens has a refractive power. For example, the second lens has a negative refractive power. The second lens has a convex surface. In an embodiment, the second lens has a convex object-side surface.

The second lens has an aspherical surface. For example, the second lens has an aspherical object-side surface. The second lens may be formed using a material having a relatively high degree of light transmittance and excellent workability. As an example, the second lens may be formed using a plastic material. The second lens has a refractive index higher than that of the first lens. In an embodiment, the refractive index of the second lens is greater than or equal to 1.6.

The third lens has a refractive power. For example, the third lens has a positive refractive power.

The third lens has an aspherical surface. In an embodiment, the third lens has an aspherical image-side surface. The third lens may be formed using a material having a relatively high degree of light transmittance and excellent workability. In an example, the third lens is formed using a plastic material. The third lens may have a refractive index substantially similar to that of the second lens. In an embodiment, the refractive index of the third lens is greater than or equal to 1.6.

The fourth lens has a refractive power. For example, the fourth lens has a positive refractive power. The fourth lens has a convex surface. In an embodiment, the fourth lens has a convex object-side surface.

The fourth lens has an aspherical surface. For example, both surfaces of the fourth lens are aspherical. The fourth lens may be formed using a material having a relatively high degree of light transmittance and excellent workability. In an example, the fourth lens is formed using a plastic material. The fourth lens has a refractive index substantially the same as that of the first lens. In an embodiment, the refractive index of the fourth lens is less than 1.6.

The fifth lens has a refractive power. For example, the fifth lens has a positive refractive power.

The fifth lens has an aspherical surface. In an embodiment, both surfaces of the fifth lens are aspherical. The fifth lens may be formed using a material having a relatively high degree of light transmittance and excellent workability. In an example, the fifth lens is formed using a plastic material. The fifth lens may have a refractive index substantially the same as that of the third lens. For example, the refractive index of the fifth lens is greater than or equal to 1.6.

The sixth lens has a refractive power. For example, the sixth lens has a negative refractive power. The sixth lens may have an inflection point. In an embodiment, the sixth lens includes one or more inflection points formed on opposing surfaces.

The sixth lens has an aspherical surface. For example, both surfaces of the sixth lens are aspherical. The sixth lens may be formed using a material having a relatively high degree of light transmittance and excellent workability. In an example, the sixth lens is formed using a plastic material. The sixth lens may have a refractive index substantially similar to that of the fifth lens. In an embodiment, the refractive index of the sixth lens is greater than or equal to 1.6.

The seventh lens has a refractive power. For example, the seventh lens has a positive refractive power. The seventh lens may have a convex surface. In an embodiment, the seventh lens has a convex object-side surface. The seventh lens may have an inflection point. For example, the seventh lens includes one or more inflection points formed on opposing surfaces.

The seventh lens has an aspherical surface. For example, both surfaces of the seventh lens are aspherical. The seventh lens may be formed using a material having a relatively high degree of light transmittance and excellent workability. As an example, the seventh lens is formed using a plastic material. The seventh lens may have a refractive index less than that of the sixth lens. In an embodiment, the refractive index of the seventh lens is less than 1.6.

Aspherical surfaces of the first to seventh lenses may be expressed by Equation 1 below.

$\begin{matrix} {Z = {\frac{{cr}^{2}}{1 + \sqrt{1 - {\left( {1 + k} \right)c^{2}r^{2}}}} + {Ar}^{4} + {Br}^{6} + {Cr}^{8} + {Dr}^{10} + {Er}^{12} + {Fr}^{14} + {Gr}^{16} + {Hr}^{18} + {Jr}^{20}}} & (1) \end{matrix}$

In Equation 1, c represents an inverse of a radius of curvature of a lens, k represents a conic constant, r represents a distance from a certain point on an aspherical surface of the lens to an optical axis, A to J represent aspherical constants, and Z (or SAG) represents a distance between the certain point on the aspherical surface of the lens at the distance r and a tangential plane meeting the apex of the aspherical surface of the lens.

The optical imaging system further includes a filter, an image sensor, and a stop. The filter is interposed between the seventh lens and the image sensor. The filter may block light having a portion of wavelengths of visible light, in order to generate a clear image. For example, the filter blocks light of an infrared wavelength.

The image sensor forms an imaging plane. As an example, a surface of the image sensor forms the imaging plane. The stop is disposed to adjust an amount of light incident on a lens. In an embodiment, the stop is interposed between the first lens and the second lens.

The optical imaging system satisfies Conditional Expressions 1 to 5 below.

FNo.≤2.09  (Conditional Expression 1)

V2+V3<V1  (Conditional Expression 2)

V5+V6<V4  (Conditional Expression 3)

CT2<0.2 mm  (Conditional Expression 4)

1.0<TTL/f  (Conditional Expression 5)

In Conditional Expressions 1 to 5, f represents an overall focal length of the optical imaging system, V1 represents an Abbe number of the first lens, V2 represents an Abbe number of the second lens, V3 represents an Abbe number of the third lens, V4 represents an Abbe number of the fourth lens, V5 represents an Abbe number of the fifth lens, V6 represents an Abbe number of the sixth lens, TTL represents a distance from an object-side surface of the first lens to an imaging plane, and CT2 represents a thickness of the second lens.

Conditional Expressions 2 to 4 are provided as parametric relationships for the miniaturization of the optical imaging system. For example, the optical imaging system satisfying one or more Conditional Expressions among Conditional Expressions 2 to 4 reduces an overall imaging distance (that is, TTL).

Subsequently, an optical imaging system according to various examples will be described. First of all, the optical imaging system according to a first example will be described with reference to FIG. 1 . An optical imaging system 100 includes a first lens 110, a second lens 120, a third lens 130, a fourth lens 140, a fifth lens 150, a sixth lens 160, and a seventh lens 170.

The first lens 110 has a positive refractive power, a convex object-side surface, and a concave image-side surface. The second lens 120 has a negative refractive power, a convex object-side surface, and a concave image-side surface. The third lens 130 has a positive refractive power, a convex object-side surface, and a concave image-side surface. The fourth lens 140 has a positive refractive power and opposing convex surfaces. The fifth lens 150 has a positive refractive power, a convex object-side surface, and a concave image-side surface. The sixth lens 160 has a negative refractive power, a convex object-side surface, and a concave image-side surface. In addition, sixth lens 160 includes inflection points formed on opposing surfaces. The seventh lens 170 has a positive refractive power, a convex object-side surface, and a concave image-side surface. In addition, seventh lens 170 includes inflection points formed on opposing surfaces.

Optical imaging system 100 further includes a filter 180, an image sensor 190, and a stop ST. Filter 180 is interposed between seventh lens 170 and image sensor 190, while stop ST is interposed between first lens 110 and second lens 120.

Optical imaging system 100 includes a plurality of lenses having relatively high refractive indices. For example, second lens 120, third lens 130, fifth lens 150, and sixth lens 160 have refractive indices greater than or equal to 1.6. In an embodiment, the refractive indices of second lens 120, third lens 130, fifth lens 150, and sixth lens 160 are greater than 1.65 and less than 2.0.

Optical imaging system 100 is configured to implement a bright optical imaging system. In detail, an F number of optical imaging system 100 is 2.09. Optical imaging system 100 has a relatively wide angle of view. For example, an overall angle of view of the optical imaging system 100 is 83.3.

Optical imaging system 100 satisfies each of Conditional Expressions 2 to 5, described above. As examples, in optical imaging system 100, the sum (V2+V3=40.7) of an Abbe number of second lens 120 (V2=20.35) and an Abbe number of third lens 130 (V3=20.35) is less than an Abbe number of first lens 110 (V1=56.11). The sum (V5+V6=40.7) of an Abbe number of the fifth lens 150 (V5=20.35) and an Abbe number of the sixth lens 160 (V6=20.35) is less than an Abbe number (V4=56.11) of the fourth lens 140. In addition, a thickness of the second lens 120 is 0.13 mm, while an imaging distance to focal length ratio (TTL/f) is 1.20.

An optical imaging system having the configuration described above has aberration characteristics as illustrated by the graphs in FIG. 2 . FIG. 3 lists aspherical characteristics of the optical imaging system according to the example. Table 1 lists lens characteristics of the optical imaging system according to the example.

TABLE 1 First Example F No. = 2.090 f = 3.4900 TTL = 4.200 Sur- Thick- face Radius of ness/ Refractive Abbe Focal No. Element Curvature Distance Index Number Length S1 First 1.3902 0.4852 1.547 56.113 3.203 S2 Lens 5.9254 0.1433 ST Stop Infinity 0.0000 S3 Second 4.5499 0.1300 1.668 20.353 −6.733 S4 Lens 2.2360 0.1251 S5 Third 4.2504 0.2259 1.668 20.353 41.230 S6 Lens 4.9191 0.1000 S7 Fourth 13.0519 0.2000 1.547 56.113 16.898 S8 Lens −31.4071 0.1680 S9 Fifth 10.936 0.2050 1.668 20.353 87.414 S10 Lens 13.3547 0.3604 S11 Sixth 13.1415 0.4077 1.668 20.353 −13.203 S12 Lens 5.2120 0.1000 S13 Seventh 1.5777 0.7175 1.537 55.656 127.157 S14 Lens 1.3586 0.1819 S15 Filter Infinity 0.1100 1.518 64.197 S16 Infinity 0.5424 S17 Imaging Infinity −0.0024   Plane

An optical imaging system according to a second example will be described with reference to FIG. 4 . An optical imaging system 200 includes a first lens 210, a second lens 220, a third lens 230, a fourth lens 240, a fifth lens 250, a sixth lens 260, and a seventh lens 270.

The first lens 210 has a positive refractive power, a convex object-side surface, and a concave image-side surface. The second lens 220 has a negative refractive power, a convex object-side surface, and a concave image-side surface. The third lens 230 has a positive refractive power, a convex object-side surface, and a concave image-side surface. The fourth lens 240 has a positive refractive power and opposing convex surfaces. The fifth lens 250 has a positive refractive power, a convex object-side surface, and a concave image-side surface. The sixth lens 260 has a negative refractive power, a convex object-side surface, and a concave image-side surface. In addition, sixth lens 260 includes inflection points formed on opposing surfaces. The seventh lens 270 has a positive refractive power, a convex object-side surface, and a concave image-side surface. In addition, seventh lens 270 includes inflection points formed on opposing surfaces.

Optical imaging system 200 further includes a filter 280, an image sensor 290, and a stop ST. Filter 280 is interposed between seventh lens 270 and image sensor 290, while stop ST is interposed between first lens 210 and second lens 220.

Optical imaging system 200 includes a plurality of lenses having relatively high refractive indices. For example, second lens 220, third lens 230, fifth lens 250, and sixth lens 260 have refractive indices greater than or equal to 1.6. In an embodiment, the refractive indices of second lens 220, third lens 230, fifth lens 250, and sixth lens 260 are greater than 1.65 and less than 2.0.

Optical imaging system 200 is configured to implement a bright optical imaging system. In detail, an F number of optical imaging system 200 is 1.89. Optical imaging system 200 has a relatively wide angle of view. For example, an overall angle of view of the optical imaging system 200 is 83.3.

Optical imaging system 200 satisfies each of Conditional Expressions 2 to 5, described above. For example, in optical imaging system 200, the sum (V2+V3=40.7) of an Abbe number of second lens 220 (V2=20.35) and an Abbe number of third lens 230 (V3=20.35) is less than an Abbe number (V1=56.11) of first lens 210. The sum (V5+V6=40.7) of an Abbe number of fifth lens 250 (V5=20.35) and an Abbe number of sixth lens 260 (V6=20.35) is less than an Abbe number of fourth lens 240 (V4=56.11). In addition, a thickness of second lens 220 is 0.144 mm, while an imaging distance to focal length ratio (TTL/f) is 1.225.

An optical imaging system having the configuration described above has aberration characteristics as illustrated by the graphs in FIG. 5 . FIG. 6 lists aspherical characteristics of the optical imaging system according to the example. Table 2 lists lens characteristics of the optical imaging system according to the example.

TABLE 2 Second Example F No. = 1.890 f = 3.3800 TTL = 4.141 Sur- Thick- face Radius of ness/ Refractive Abbe Focal No. Element Curvature Distance Index Number Length S1 First 1.3852 0.4985 1.547 56.113 3.165 S2 Lens 6.0739 0.1481 ST Stop Infinity 0.0000 S3 Second 4.7250 0.1436 1.668 20.353 −6.656 S4 Lens 2.2628 0.1242 S5 Third 3.7948 0.2133 1.668 20.353 38.588 S6 Lens 4.3497 0.0918 S7 Fourth 10.9431 0.1985 1.547 56.113 17.363 S8 Lens −70.9467 0.1687 S9 Fifth 9.241 0.2218 1.668 20.353 68.063 S10 Lens 11.4872 0.3649 S11 Sixth 12.8242 0.4171 1.668 20.353 −12.887 S12 Lens 5.0838 0.0868 S13 Seventh 1.5712 0.7230 1.537 55.656 125.277 S14 Lens 1.3503 0.2087 S15 Filter Infinity 0.1100 1.518 64.197 S16 Infinity 0.4205 S17 Imaging Infinity 0.0014 Plane

An optical imaging system according to a third example will be described with reference to FIG. 7 . An optical imaging system 300 includes a first lens 310, a second lens 320, a third lens 330, a fourth lens 340, a fifth lens 350, a sixth lens 360, and a seventh lens 370.

The first lens 310 has a positive refractive power, a convex object-side surface, and a concave image-side surface. The second lens 320 has a negative refractive power, a convex object-side surface, and a concave image-side surface. The third lens 330 has a positive refractive power, a convex object-side surface, and a concave image-side surface. The fourth lens 340 has a positive refractive power and opposing convex surfaces. The fifth lens 350 has a positive refractive power, a convex object-side surface, and a concave image-side surface. The sixth lens 360 has a negative refractive power, a convex object-side surface, and a concave image-side surface. In addition, sixth lens 360 includes inflection points formed on opposing surfaces. The seventh lens 370 has a positive refractive power, a convex object-side surface, and a concave image-side surface. In addition, seventh lens 370 includes inflection points formed on opposing surfaces.

Optical imaging system 300 further includes a filter 380, an image sensor 390, and a stop ST. Filter 380 is interposed between seventh lens 370 and image sensor 390, while stop ST is interposed between first lens 310 and second lens 320.

Optical imaging system 300 includes a plurality of lenses having relatively high refractive indices. For example, second lens 320, third lens 330, fifth lens 350, and sixth lens 360 have refractive indices greater than or equal to 1.6. In detail, the refractive indices of second lens 320, third lens 330, fifth lens 350, and sixth lens 360 are greater than 1.65 and less than 2.0.

Optical imaging system 300 is configured to implement a bright optical imaging system. In detail, an F number of optical imaging system 300 is 1.89. Optical imaging system 300 has a relatively wide angle of view. For example, an overall angle of view of the optical imaging system 300 is 85.2.

Optical imaging system 300 satisfies each of Conditional Expressions 2 to 5, described above. For example, in optical imaging system 300, the sum (V2+V3=40.7) of an Abbe number of second lens 320 (V2=20.35) and an Abbe number of third lens 330 (V3=20.35) is less than an Abbe number of first lens 310 (V1=56.11). The sum (V5+V6=40.7) of an Abbe number of fifth lens 350 (V5=20.35) and an Abbe number of sixth lens 360 (V6=20.35) is less than an Abbe number of fourth lens 340 (V4=56.11). In addition, a thickness of second lens 320 is 0.158 mm, while an imaging distance to focal length ratio (TTL/f) is 1.223.

An optical imaging system having the configuration described above has aberration characteristics, as illustrated by the graphs in FIG. 8 . FIG. 9 lists aspherical characteristics of the optical imaging system according to the example. Table 3 lists lens characteristics of the optical imaging system according to the example.

TABLE 3 Third Example F No. = 1.890 f = 3.7200 TTL = 4.551 Sur- Thick- face Radius of ness/ Refractive Abbe Focal No. Element Curvature Distance Index Number Length S1 First 1.5238 0.5483 1.547 56.113 3.481 S2 Lens 6.6813 0.1629 ST Stop Infinity 0.0000 S3 Second 5.1975 0.1579 1.668 20.353 −7.322 S4 Lens 2.4891 0.1366 S5 Third 4.1742 0.2347 1.668 20.353 42.448 S6 Lens 4.7846 0.1010 S7 Fourth 12.0374 0.2184 1.547 56.113 19.099 S8 Lens −78.0414 0.1856 S9 Fifth 10.165 0.2440 1.668 20.353 74.869 S10 Lens 12.6359 0.4014 S11 Sixth 14.1066 0.4588 1.668 20.353 −14.176 S12 Lens 5.5922 0.0955 S13 Seventh 1.7283 0.7953 1.537 55.656 137.796 S14 Lens 1.4853 0.2087 S15 Filter Infinity 0.1100 1.518 64.197 S16 Infinity 0.4907 S17 Imaging Infinity 0.0014 Plane

As set forth above, according to examples, an optical imaging system capable of capturing a distant image and being mounted in a small terminal may be provided. While this disclosure includes specific examples, it will be apparent after an understanding of this disclosure that various changes in form and details may be made in these examples without departing from the spirit and scope of the claims and their equivalents. The examples described herein are to be considered in a descriptive sense only, and not for purposes of limitation. Descriptions of features or aspects in each example are to be considered as being applicable to similar features or aspects in other examples.

Suitable results may be achieved if the described techniques are performed in a different order, and/or if components in a described system, architecture, device, or circuit are combined in a different manner, and/or replaced or supplemented by other components or their equivalents. Therefore, the scope of the disclosure is defined not by the detailed description, but by the claims and their equivalents, and all variations within the scope of the claims and their equivalents are to be construed as being included in the disclosure. 

What is claimed is:
 1. An optical imaging system comprising: a first lens having a positive refractive power; a second lens having a refractive power; a third lens having a refractive power; a fourth lens having a convex object-side surface along an optical axis of the optical imaging system; a fifth lens having a positive refractive power; a sixth lens having a convex object-side surface along the optical axis; and a seventh lens having a convex object-side surface along the optical axis, wherein the first to seventh lenses are sequentially disposed in ascending numerical order along the optical axis from an object side of the optical imaging system toward an imaging plane of the optical imaging system, the optical imaging system has a total number of seven lenses having a refractive power, the second lens has a refractive index greater than or equal to 1.65, and an F number of the optical imaging system is less than or equal to 2.09.
 2. The optical imaging system of claim 1, wherein the first lens has a convex object-side surface along the optical axis.
 3. The optical imaging system of claim 1, wherein the first lens has a concave image-side surface along the optical axis.
 4. The optical imaging system of claim 1, wherein the second lens has a convex object-side surface along the optical axis.
 5. The optical imaging system of claim 1, wherein the second lens has a concave image-side surface along the optical axis.
 6. The optical imaging system of claim 1, wherein the sixth lens has a concave image-side surface along the optical axis.
 7. The optical imaging system of claim 1, wherein the seventh lens has a concave image-side surface along the optical axis.
 8. An optical imaging system comprising: a first lens having a positive refractive power; a second lens having a refractive power; a third lens having a refractive power; a fourth lens having a refractive power; a fifth lens having a positive refractive power; a sixth lens having a negative refractive power and a convex object-side surface along an optical axis of the optical imaging system; and a seventh lens having a convex object-side surface along the optical axis, wherein the first to seventh lenses are sequentially disposed in ascending numerical order along the optical axis from an object side of the optical imaging system toward an imaging plane of the optical imaging system, the optical imaging system has a total number of seven lenses having a refractive power, a radius of curvature of an image-side surface of the first lens at the optical axis is greater than a radius of curvature of an image-side surface of the third lens at the optical axis, the second lens has a refractive index greater than or equal to 1.65, and an F number of the optical imaging system is less than or equal to 2.09.
 9. The optical imaging system of claim 8, wherein the first lens has a convex object-side surface along the optical axis.
 10. The optical imaging system of claim 8, wherein the first lens has a concave image-side surface along the optical axis.
 11. The optical imaging system of claim 8, wherein the second lens has a convex object-side surface along the optical axis.
 12. The optical imaging system of claim 8, wherein the second lens has a concave image-side surface along the optical axis.
 13. The optical imaging system of claim 8, wherein the third lens has a convex object-side surface along the optical axis.
 14. The optical imaging system of claim 8, wherein the sixth lens has a refractive index greater than or equal to 1.65. 